I think it's not very obvious that you need to collect certain things to unlock new Skills in the skill tree (O). We'll probably add some tooltips to make that more obvious. After unlocking the other skills you'll be able to craft more things at the workbench.
The Rocket Site and other parts are not interactable unless you finish the rocket. For now every part of the Rocket are crafted at the workbench.
Thanks for your feedback.